Some applications call for retarding the relative rotation of two members to maintain rotation below a predetermined speed. One of the most common examples is a vehicle glove compartment lid. For example, when the lock is clicked open, some lids are opened automatically by a spring, which is loaded when the lid is pushed shut by the user; in which case, the retarding device prevents the lid from springing open violently. In other cases, the lid is lifted open by the user and clicked into a limit position, normally defined by a stop mechanism; in which case, the retarding device prevents the lid from dropping down sharply into the closed position (under its own weight and/or by the thrust exerted by a contrast spring) when the stop mechanism is released.
The above problems are currently solved using retarding devices which are either fitted to the hinges or connected to the moving member, and which provide, in a controlled manner, for braking rotation either in both (open and closed) directions or only in, the direction of sharp or accelerated movement which might endanger the safety of the user. Retarding devices are substantially of two types. A first type comprises a friction mechanism (normally mechanical) normally having facing spring-loaded friction members which rub against each other during the movement to be retarded, so that part of the energy produced during the movement must overcome the friction between the friction members, thus greatly reducing the force applied to, and acceleration of, the moving member. A second type comprises a hydraulic mechanism in which one or more gears, connected to the moving member to be braked, are immersed and rotated in a thick fluid (e.g., silicone oil).
Retarding devices of both above types have numerous drawbacks: both are expensive and bulky, and neither can be integrated with the hinge structure. Moreover, friction devices are mechanically complex, not always reliable, and subject to wear; while hydraulic devices are subject to leakage, and, above all, vary in performance according to ambient temperature (which affects the density of the oil and hence the extent to which the movement is retarded).